1. Field of the Invention
The present invention relates to a device for detecting the level of a liquid filled in an opaque receptacle such as a metallic receptacle without any contact with the liquid.
2. Description of the Related Prior Art
A liquid such as refreshing drink syrup and beer is filled in a hermetically sealed receptacle such as a tank and container. A desired amount of the liquid in the receptacle is taken out and consumed through a tap of the receptacle.
This type of hermetically sealed receptacle is normally made of a metal to prevent the quality of the liquid in it from deteriorating, and therefore, the liquid in the receptacle cannot be seen from outside. For this reason, a manager of the receptacle has to guess the remaining volume of the liquid inside by using his head, or infer the remaining volume from the weight of the receptacle by placing it on a balance.
However, the above-mentioned manner for detecting the remaining volume is extremely unreliable and is cumbersome for the manager, and the manager is apt to neglect checking the remaining amount in the receptacle. As a result, it is not until the liquid in the receptacle runs out that the manager comes to know that there is no liquid left, that is, the receptacle is empty.
As a solution to such a problem, it is considered to use a hermetically sealed receptacle incorporating a device for detecting the liquid level. However, this is not feasible because it would be necessary to replace all existing receptacles with those provided with such detecting devices. Additionally, some types of detecting devices have sensor units that are designed to directly contact a liquid in a receptacle. Such detecting devices cannot be used when the liquid is food.